When drilling a well it is desirable to know the path of the borehole that has been drilled. In open hole, where there is no steel casing lining the borehole, the existing method of positioning is to use 3 measurements: measured depth along the borehole from surface, inclination of the borehole to vertical and a measurement of magnetic north taken from a magnetometer. These sensors are placed in non-magnetic housings.
In cased hole operations, or with ferro-magnetic tool housings, it is necessary to use a gyroscope (gyro) sensor in place of the magnetometer to determine position in relation to north because it is not affected by magnetic effects. It is in cased boreholes that gyro's are most beneficial, but they may be used in any configuration of borehole. The existing methods use inertial grade mechanical gyros (rotating mass) which are expensive, susceptible to mechanical shock, have a limited product lifespan of a few thousand hours and require complicated electronic interfaces.